For example, when a porcupine encounters a predator, its long sharp pointed hairs will stand up as a means of 20 .
答案：(D) scaring the enemy
語意「牠尖銳的長毛會豎起來，作為『嚇退敵人』的手段」，scaring the enemy 符合，呼應前文提到豪豬遇到掠食者時的反應；blocking the smell（阻擋氣味）、attracting mates（吸引配偶）、showing friendliness（表現友善，語意相反）都不合。
本題大考中心未公布逐題答對率，以下不談數據，只談觀念。
四個選項都是動名詞片語，中文差很遠，照理不難分；但如果沒把前一句一起讀，會不確定豪豬豎起尖刺到底是為了什麼。
四個選項都是動名詞片語，可見這一格考的是語意，那就往前讀。前一句是 Many mammals fluff up their fur when threatened, to look bigger and thus more dangerous.（許多哺乳類受到威脅時會把毛蓬起來，讓自己看起來更大、更危險。）——這一句已經把目的講清楚了：讓自己看起來更嚇人。本句是這個通則的具體例子：when a porcupine encounters a predator, its long sharp pointed hairs will stand up as a means of ___（豪豬遇上掠食者時，牠又長又尖的刺會豎起來，作為……的手段）。既然前一句說目的是 more dangerous、而這一句的對象是 predator（掠食者），豎刺當然是為了嚇退敵人，填 scaring the enemy。
attracting mates（吸引配偶）：本句的對象是掠食者不是同類，而且前一句講的是自保不是求偶。showing friendliness（表示友善）：方向完全相反。blocking the smell（阻擋氣味）：整段沒有提到氣味。
as a means of（作為……的手段）、scare sb away（嚇跑某人）、a predator（掠食者）、stand up（豎起）、for example（舉例來說）、trap air（把空氣困住）。
Goose bumps are one of those fight-or-flight reactions of the sympathetic nervous system. When you experience cold or fear, a nerve reaction is sent to the muscles, which then contract involuntarily. This muscle contraction causes your body hair to stand erect. The skin with standing body hair 16 a goose's skin after its feathers have been plucked—hence the name goose bumps. But 17 is this helpful to us as a response to fear or cold?
Back in the days when our ancestors may have had a lot more body hair, this might have helped to keep them warm or scare an oncoming predator. These days, however, goose bumps are 18 to human beings.
Goose bumps, or the reflex that causes them, also occur in many other mammals. Many mammals fluff up their fur when 19 , to look bigger and thus more dangerous. For example, when a porcupine encounters a predator, its long sharp pointed hairs will stand up as a means of 20 . In animals with a thick hair coat, the rising of hair traps more air between the hairs, providing another layer of insulation to keep them warm.